Taxpayers' money is being used to both prosecute and defend the case, which was brought by Patricia Lewsley, the Northern Ireland Commissioner for Children and Young People (NICCY), and has been in the courts since 2006.

In December, a judge rejected the attempt to ban smacking but Ms Lewsley appealed the decision – a process that is expected to last until the autumn.

The prosecution has been funded from the £1.9 million NICCY annual budget, while the defence costs have been borne by the Department of Finance and Personnel (DFP).

Figures released to the Assembly show that NICCY spent more than £36,000 bringing the initial case and DFP said it spent more than £52,000 defending that case.

The costs of the current appeal are not yet known.

Describing herself as "the only champion children and young people have", Ms Lewsley said at the time that children's "basic right to be protected from harm" was being breached when they were smacked.

But last night the TaxPayers' Alliance said it was wrong for taxpayers money to be "squandered" on lawyers — especially when it is an issue that "should be decided by parents".

And DUP children's spokeswoman Michelle McIlveen said that she had concerns about the costs of the legal bid by Ms Lewsley, a former SDLP Assemblywoman.

Mark Wallace, campaign director of the TaxPayers' Alliance, said: "It's completely wrong for taxpayers' money to be wasted on high-charging lawyers like this, especially when it is an issue that should be decided by parents.

"The commissioner would make more of a difference to children's lives by letting families keep their hard-earned money and spend it as they wish, rather than squandering our taxes.

"We pay taxes for essential services, not for bureaucrats to fight never-ending legal campaigns."

And Miss McIlveen — who uncovered the prosecution costs in the Assembly — said that the taxpayer would lose, irrespective of who won the case.

"No matter what the outcome of the appeal it will be the taxpayer who will be the loser," she said.

"NICCY is funded by the public money and, as with every publicly-funded body, has a duty to be circumspect about how this money is spent.

"This (smacking) legislation was introduced to bring us into line with the rest of the UK.

"The primary legislation on which it is based was deliberated over carefully in both Houses of Parliament; there was extensive consultation on the issue and there has been a High Court ruling on the application for judicial review.

"I am somewhat concerned that costs are continuing to mount."

Ruling against the commissioner in the initial judicial review, Mr Justice Gillen said: "The current legislation strictly confines the severity of corporal punishment which a parent may lawfully give to a child."

A spokesman for NICCY said it did not want to comment on the costs while the case was ongoing.